Investigations were continuing today into a medical trial that went disastrously wrong, leaving six previously healthy men seriously ill in hospital.

Two of the men are critically ill and the other four are still in a "serious" condition in a London hospital.

A drugs company last night apologised to the men's families.

The drug, known as TGN1412, is made by pharmaceutical company TeGenero AG. It is intended to fight leukaemia, rheumatoid arthritis and multiple sclerosis.

One of two trial volunteers who escaped unscathed after being given a placebo described the horrific scene. Raste Khan, 23, told a national newspaper: "First they began tearing their shirts off complaining of fever, then some screamed out that their heads felt like they were going to explode."

Another national newspaper reported senior doctors were concerned all six victims had been given the drug at the same time - which it said went against medical guidance.

Chief scientific officer of TeGenero AG, Thomas Hanke, pictured, said he was "devastated". Asked whether TeGenero AG had apologised to the families, he replied: "Yes."

Parexel, the company running the trial, said it had operated within regulatory guidelines.